Temperature compensated thermal power relay



May 10, 1960 .1. H. GREIG 2,936,354

TEMPERATURE COMPENSATED THERMAL POWER RELAY Filed June 3, 1959 OPERATED OPERATING CIRCUIT CIRCUIT INVENTOR JOHN H. GREIG lalwz ATTORNEY.

United States Patent TEMPERATURE COMPENSATED THERMAL POWER RELAY Application June 3, 1959, Serial No. 817,840 7 Claims. (Cl. 200-122 invention concerns a temperature compensated time delay thermal power relay.

Thermal power relays heretofore known foruse in street light switching systems and similar applications have in common the use of a heater coil wound on a bimetallic element with another bimetallic element associated therewith in such a way as to provide some compensation for variations in ambient temperatures. One such known relay has the bimetallic temperature responsive element and the compensator element secured together at one end by a pivoted mounting. The other ends of the two elements are held between an adjusting screw and a pushbutton snap action power switch. The sensitivity of this relay is limited or reduced by the unavoidable friction in the pivot of the mounting. The temperature compensation is not perfect because the distance between the bimetallic elements does not remain constant with changes in temperature.

,In another known relay, two bimetallic elements are fastened with eyelets to an insulating spaced with a snap action spring mounted at the center of the temperature compensating element and with the heater carried on the other, temperature responsive element. This structure requires that a high current from the controlled circuit passthroughthe bimetallic material. This passage of current through the bimetallic material is undesirable because the compensating elements becomes heated. Also the location of the snap action spring at the center of the compensating element results in imperfect temperature compensation.

' The present invention is directed at overcoming the difficulties and disadvantages of prior temperature compensated time delay relays to provide perfect temperature compensation with any change in ambient temperature. According to the invention there is provided a main active temperature responsive bimetallic element in thermal contact witha heater and carrying an adjustment screw. This element is secured to a spacer which in turn is secured" to two temperature compensating bimetallic elements. The compensating elements in turn are secured in spaced relation to a base such as a chassis plate. A snap action switch has its button disposed for contact by the adjustment screw. Heating power is supplied to the heater causing the main active temperature responsive element to bend so that the screw operates the switch. Temperature compensation due to changes in ambient temperaturesis obtained by bending of the compensating elements and is rendered perfect by the spherically curved end of the screw which provides a bearing surface. The invention does not require any pivotal attachment between the bimetallic elements, thus avoiding a troublesome source 20f friction. No electric current passes through the bimetallic material so that low conductivity bimetallic material can be used, heat conduction losses are avoided and power supplied to the heater is conserved. It is therefore a principal object of the invention to provide av thermal power relay having a switch operating memberadjustably carried by an activethermally responsive bimetallic .element,said member having a rounded cam bearing end adapted to actuate a switch button. 1

It is another object to provide a thermal power relay with a switch operating member carried by an active bimetallic element, said member having a cam end which is spherically curved, the cam end being thus adapted to remain in constant contact with a push-button of a switch in' all temperature compensated positions of bending assumed by the bimetallic element with respect to a pair of temperature compensating bimetallic elements.

It is another object to provide a thermal delay relay with an assembly of an active temperature responsive bimetallic element and two temperature compensating bimetallic elements, the latter two elements taking up the mechanical strain imposed by actuation of a switch by the main element, and providing increased stiffness to the assembly.

A still further object is provision of a thermal delay relay with an active temperature responsive bimetallic element carrying a heater and an adjustment member formed with a cam end, and with two temperature compensating bimetallic elements spaced from and rigidly assembled with the active element, the cam end being shaped to retain contact with a pushbutton of a switch in all positions of bending assumed by the active element with respect to the compensating elements.

Other and further objects and advantages of the invention will become apparent from the following detailed description taken together with the drawing, wherein:

Fig. 1 is a side elevational view of a relay assembly embodying the invention, including schematic representations of circuit connections.

Fig. 2 is a top plan view of the assembly of Fig. 1.

Fig. 3 is a perspective view on an enlarged scale of the relay per se.

Fig. 4 is a sectional view on an enlarged scale taken on line 4-4 of Fig- 2.

Fig. 5 is a sectional view on a further enlarged scale of the end of a switch operating member employed on the relay.

Fig. 6 is a diagram employed in explaining the invention.

Referring to Figs. 1-5, there is shown a relay having two flat laminated bimetallic strips or elements 10, 12 which serve as temperature compensating elements for a bimetallic element 14. Element 14 is also a flat laminated metal stripon which is slidably and adjustably mounted a rectangular, tubular heater element 16. This heater contains a coil of resistance wire which is electrically energized via terminal wires 20, 22. The wires 20, 22 are in circuit with an operating circuit 23 and a a suitable power supply such as battery 21. Element 14 carries a cylindrical switch operating member 24 at its free end. This member may be an adjustably mounted screw threaded in a hole 26 in element 14. Element 14 is secured to and supported on a flat, rectangular spacer plate 28 by a rivet 30. The spacer plate is supported by and secured to one end of each of elements 10 and 12 by rivets 32, 34. The element 14 and elements 10, 12 are spaced by the thickness of plate 28, the spacing providing room for the heater 16 mounted on element 14. The forward free ends of the elements 10 and 12 are secured to a base plate or chassis frame36 by rivets 38 inserted in holes 39. The ends of elements 10 and 12 are spaced from plate 36 by spacers 40, 42 a short distance above plate 36. A conventional type of snap action switch 44 is secured to the base plate by screws 45, 47 and is spaced from the underside of the plate 36 by spacer members 48. The threaded shank of adjustment screw 24 passes through a hole 50in plate 36 and contacts an upwardly extending pushbutton 52 on the switch. A nut 54 locks the adjustment screw in position on element 14.

Patented May 10, 1960 The button 52 is preferably formedwith a rounded tip 55 against which bears the lower free end 56 of member 24. This end 56 is formed with a rounded, spherically curved surface as shown in Fig. 5, adapted tocam on tip ly pressing the end 56 of the screw 24 against the tip of button 52. for operating the switch. The switch has leads 60, 62 terminating in an external circuit 61 operated by the switch. Temperature compensation of the relay is required to prevent ambient temperature changes from bending the member 14 down or up and operating the relay or preventing it from operating respectively. This compensation is efiected by elements and 12, and the compensation is corrected precisely and perfectly by the properly shaped cam end 56 of screw 24. The bimetallic elements 10, 12 are so oriented with respect to element 14, that they bend up to raise the spacer plate 28 when the relay temperature is reduced, while the element 14 also bends up at its end on spacer 28. The result is that the screw 24 remains substantially in a fixed position with respect to the switch button 52. Since the element 14 and the compensating elements 10 and 12 are not in the same plane, a slight movement of screw 24 does take place with respect to the tip 55v of button 52. However the member 24 is so constructed that during this movement its end 56 never loses contact with tip 55 nor does it depress the button 52. Thus the structure provides correction to perfection of the temperature compensation movements of the relay elements. This may be best understood by reference to Fig. 6.

The bending of the elements 10, 12 and 14 is exaggerated in Fig. 6 to illustrate the action more clearly. Each of the element 10, 12 and 14 bend when their temperature changes to form arcs of circles. Element 12 is not shown in Fig. 6 but it will be understood that element 12 bends like element 10 and remains parallel to it. Elements It}, 12 and 14 are of the same length and thickness and define arcs of circles having equal radii of curvature, R and R respectively. Space S represents the thickness of spacer plate 28. S is the fixed distance of separation of the ends of elements 10, 12 and 14 at plate 28. The free end of element 14 moves relative to button 52 a distance Y in a vertical plane perpendicular to element 14 and a distance X in the horizontal plane parallel to plate 28. From the geometry of the device:

X :5 sin A and Y=S cos A where A is the angle subtended by the arcuately bent elements 10, 12 and 14. Then:

X +Y ==S (sin Al-l-cos A) and since sin A-l-cos A=1 2+ 2 2 The last equation defines the locus L of the path of movement of the end of screw 24. Thislast equation is that of a circle of radius S. By forming the end 56 of screw 24 as a portion of a sphereof radius S'=S, perfect correction is effected for all temperature compensation movements of the end of screw 24 with respect to the tip 54 of buton 52. Thus the screw end 56 never loses contact with tip 54 and never depresses the button undseirably due to ambient, accidental and random temperature changes of the several bimetallic elements. The correction for relative movements of the elements it), 12 and 14 due to temperature compensation is thus rendered perfect. Under normal conditions, an actuation current will beapplied to heater 16 4 via leads 20 and. 22. Element 14 will be heated. and will bend down to operate the. switch 44.

An important feature of the present invention is the use of two spaced bimetallic elements 10 and 12 as compensating elements. By using two such elements rather than one compensation element as has been done heretofore, increased stilfness is'obtained in the bimetallic element assembly which is utilized as follows. A force of certain magnitude is required to move the switch button 52 in operating the switch 44. The reaction to this force tends to bend elements 10, 12 and 14. Since two compensating elements are used instead of one an increased in stiffness of as much as 50% is obtained in the assembly without requiring an increase in the size of the active element 14. As a result a smaller heater 16 can be used and less externally applied electric power is required to operate the relay. This is an important consideration if the external source is a battery as'indicated at 21, requiring minimum current drain 'tobbtaih extensive active life. The use of the two'compen'sating elements quirement for a smaller and less expensive heater and external power supply, longer life for'the power supply,

and also results in a smaller and more compact relay assembly by permitting reduced spacing between elements 1t), 12 and 14. This is an important factor where installation space for the relay is severely limited. It will be noted that no electric current is required-to pass through the bimetallic elements. "There is thus avoided undesirable heating of the temperature respon sive bimetallic elements dependent upon the current'i'n the controlled circuit. Also the bimetallic elements can have high electrical and thermal resistivity. Thus there will be avoided the heat losses heretofore encountered in prior known relays in which the heating curfenfp'asses through one or more bimetallic elements. A" smaller heater element 16 and smaller power supply 21 therefore can be provided which is most dseirable as pointed out above.

What is claimed and sought to be protected by Letters Patent of the United States is: l. A thermal power relay assembly, comprising a base, a pushbutton switch secured to saidbase,'a pair of spaced bimetallic elements secured at one end-to said base, a support secured to the other ends of said ele ments, a third bimetallic element disposed between said pair of elements and secured at one end thereof to said support, a heater carried by the 'third element, said heater being spaced from the pair of elements a sufiicient distance to avoid heating the same, a generally cylindrical member supported at and projecting from the other end of the third element, said member having .a curved end contacting the button for operating the same, said pair of elements providing compensation for ambient temperature changes of the third element and providing increased stiffness and resistance to bending when said switch is operated by bending of the third element upon heating by said heater, said curved end ofsaid member providing correction for relative movements between, the

third element and said pair of elements due to temperature compensation therebetween, said support having a predetermined thickness, said pair of elements being secured at one side of the support, the third element being secured at the other side of the support, the'curvature of said end having a radius equal to-the thickness of said support. I

2. A thermal power relay assembly, comprising a base, a pushbutton switch secured to said base, a pair of spaced bimetallic elements secured at one end to said base, a support secured to the other ends of said elements; a third bimetallic element disposed between said pair of elements and secured at one end thereof to said support, a heater carried by the third element, said heater being spaced from the pair of elements a sufiicient distance to avoid heating the same, a generally cylindrical member sup- 10, 12 results quite unexpectedly in -the rported at and projecting from the other end of the third element, said member having a curved end contacting the button for operating the same, said pair of elements providing compensation for ambient temperature changes of the third element and providing increased stiffness and resistance to bending when said switch is operated by bending of the third element upon heating by said heater, said curved endof said member providing correction for relative movements between the third element and said pair of elements due to temperature compensation therebetween, said pair of elements and said third element being spaced apart a fixed distance on said support, the curvature of said end being spherical and having a radius equal to said fixed distance, whereby said correction is rendered perfect.

3. A thermal power relay, comprising an active thermally responsive bimetallic element, a heater carried by said element, a support, said element being secured at one end thereof to said support, a pair of other bimetallic elements secured to said support and spaced from the active element a sufiicient distance from the heater to be unheated thereby, said other elements providing temper-ature compensation for the active element, and a generally cylindrical member supported at and projecting from the other end of said active element, said member having a rounded end for contacting a button of a switch to be operated by said member, said rounded end providing correction for relative movements between the active element and said pair of elements, said pair of elements being flat metal strips disposed in coplanar relationship on said support, said active element being a fiat metal strip disposed in a plane having a fixed spacing from the plane of said pair of elements, said fixed spacing being equal to the radius of curvature of said rounded end of said member, whereby said correction is rendered perfect.

4. A thermal power relay according to claim 3, wherein said member is a screw adjustably mounted and secured on said active element.

5. A thermal power relay assembly, comprising a base,

a pushbutton switch secured to said base, a pair of spaced bimetallic elements secured at one end to said base, a support secured to the other ends of said elements, a third bimetallic element disposed between said pair of elements and secured at one end thereof to said support, a heater carried by the third element, said heater being spaced, from the pair of elements a sufficient distance to avoid heating the same, a generally cylindrical member supported at and projecting from the other end of the third element, said member having a curved end contacting the button for operating the same, said pair of elements providing compensation for ambient temperature changes of the third element and providing increased stifiness and resistance to bending when said switch is operated by bending of the third element upon heating by said heater, said curved end of said member providing correction for relative movements between the third element and said pair of elements due to temperature compensation therebetween, said pair of elements being fiat metal strips disposed in a plane at said other ends thereof, said third element being a fiat metal strip disposed in another plane at said one end thereof, the planes being spaced a fixed distance apart, the curved end of said member having a radius of curvature equal to said fixed distance, said member being a screw adjustably secured to said other end of the third element.

6. A thermal power relay assembly according to claim 5, wherein said planes are at opposite sides of said support, said support being a flat plate.

7. A thermal power relay assembly according to claim 6, wherein said heater is a tubular member adjustably and slidably mounted on said third element.

References Cited in the file of this patent UNITED STATES PATENTS 1,500,268 Replogle July 18, 1924 2,171,895 Sardeson Sept. 5, 1939 2,284,383 Elmer May 26, 1942 2,289,645 Geistert July 14, 1942 2,565,631 Sander Aug. 28, 1951 

